Caption: White beaked dolphin (Lagenorhynchus albirostris) sounds, wavelet graph. This image was produced by converting the frequencies of sounds made by a white beaked dolphin into a graph using a mathematical process known as wavelets. Wavelets reveal structure and detail that are not always visible in standard graphs of frequency over time (known as a spectrogram). This image has been plotted as a polar coordinate (circular) graph but wavelet graphs can also be in rectangular form. Dolphins produce a wide variety of high frequency vocalisations, such as clicks, whistles and cries. These sounds are used for echolocation and communication with other dolphins. They can be recorded using underwater hydrophones. Image created by Mark Fischer from Aguasonic Acoustics, USA.